Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_538_Библиотеки_им_академика_М_И_Перельмана.pdf
4
ani muscle
Exter
Longitudinal muscle
Circular muscle
Valve of Houston
J. C. Carmichael and S. Mills
Peritoneal reflection
Conjoined longitudinal muscle
Internal anal sphincter muscle
Dentate line
nal anal sphincter muscle
Corrugator cutis ani muscle
Anoderm
Fig. 1.1 Anal canal
ATZ is the area in which the majority of human
papillomavirus- related dysplastic lesions are found in the
anal canal [7]. The columns of Morgagni are noted in this
area where redundant columns of tissue are noted with anal
crypts at their base. This forms the rippled dentate line (or
pectinate line) which can be most easily identied by locating the anal crypts at the base of the anal columns (columns
of Morgagni). Anal crypts are connected to underlying anal
glands which are the presumed source of sepsis in the majority of anorectal abscesses and stula. On average, there are
six anal glands surrounding the anal canal (range, 3–12) [6,
8, 9], and they tend to be more concentrated in the posterior
quadrants. More than one gland may open into the same
crypt, and some crypts may not be connected to anal glands.
The anal gland ducts proceed inferior and lateral from the
anal canal and enter the submucosa where two-thirds enter
the internal anal sphincter and half terminate in the intersphincteric plane [8]. It is theorized that obstruction of these
ducts leads to anal abscess and stula [6]. Knowledge of the
anatomy also explains why the internal opening of a “cryptoglandular” anal stula should typically be at the dentate
line.
Distal to the dentate line, the anoderm begins and extends
for approximately 1.5 cm. According to Milligan and
Morgan, anoderm or “anal canal skin… has the structure of
skin, but there are no hairs and sweat glands and it consists
of modied squamous transitional epithelium” [10]. In other
Column of Morgagni
Iliococcygeus
Pubococcygeus
Puborectalis
Anal crypt
Anal gland
Intersphincteric groove
Anal verge
Levator
words, anoderm has squamous histology and is devoid of
hair, sebaceous glands, and sweat glands. At the anal verge,
the anal canal lining becomes thickened and pigmented and
contains hair follicles– this represents normal skin.
The dentate line represents a true division between embryonic endoderm and ectoderm. Proximal to the dentate line,
the innervation is via the sympathetic and parasympathetic
systems, with venous, arterial, and lymphatic drainage associated with the hypogastric vessels. Distal to the dentate line,
the innervation is via somatic nerves with blood supply and
drainage from the inferior hemorrhoidal system.
Internal Anal Sphincter
The internal anal sphincter (IAS) is the downward continuation of the circular smooth muscle of the rectum and terminates with a rounded edge approximately 1cm proximal to
the distal aspect of the external anal sphincter. 3D imaging
studies of this muscle demonstrate the overall volume does
not vary according to gender, but the distribution is different
with women tending to have a thicker medial/distal internal
anal sphincter [11]. Overall, the IAS was found to be approximately 2mm in thickness and 35mm in length. The authors
note that on any study, it is difcult to identify the proximal
portion of the IAS as it is a continuation of the wall of the
lower rectum.
1 Anatomy andEmbryology oftheColon, Rectum, andAnus
5
Conjoined Longitudinal Muscle
The anatomy and function of the perianal connective tissue
is often overlooked but plays a signicant role in normal
anorectal function. Measuring approximately 0.5 mm to
2.0mm in thickness, the conjoined longitudinal muscle (or
conjoined longitudinal coat) lies in between the internal and
external anal sphincters. It begins at the anorectal ring as an
extension of the longitudinal rectal muscle bers and
descends caudally joined by bers of the puborectalis muscle [12]. At its most caudal aspect, some of the conjoined
longitudinal muscle bers (referred to as corrugator cutis
ani muscle) traverse the distal external anal sphincter and
insert into the perianal skin, and some enter the fat of the
ischiorectal fossa. Fibers of the conjoined longitudinal muscle also pass obliquely and caudally through the internal
anal sphincter to interlace in a network within the subepithelial space. These subepithelial smooth muscle bers were
originally described by Treitz in 1853 [13] and have been
referred to as Treitz’s muscle. They have also been referred
to as corrugator cutis ani, musculus submucosae ani, muco-
sal suspensory ligament, and musculus canalis ani [14]. It
has been hypothesized by Thomson that disruption of
Treitz’s muscles results in anal cushion prolapse, vascular
outow obstruction, and hemorrhoidal bleeding and thrombosis [15]. Haas and Fox have hypothesized that the conjoined longitudinal muscle, and the network of connective
tissue that it supports, plays a role in minimizing anal incontinence after sphincterotomy [12].
External Anal Sphincter
The external anal sphincter (EAS) is composed of striated
muscle that forms an elliptical tube around the internal anal
sphincter and conjoined longitudinal muscle. As it extends
beyond the distal most aspect of the internal anal sphincter,
the intersphincteric groove is formed. At its distal most
aspect, corrugator cutis ani muscle bers from the conjoined
longitudinal muscle traverse the external anal sphincter and
insert into the perianal skin. Milligan and Morgan described
the external anal sphincter as having three distinct divisions
from proximal to distal that were termed sphincter ani externus profundus, supercialis, and subcutaneous [1]. With
time, this theory of three distinct divisions was proven invalid
by Goligher who demonstrated that the external anal sphincter was truly a continuous sheet of skeletal muscle extending
up to the puborectalis and levator ani muscles [16]. While the
external anal sphincter does not have three distinct anatomic
layers, it is common to see the proximal portion of the EAS
referred to as deep EAS, the midportion as the supercial
EAS, and the most distal aspect as the subcutaneous
EAS.The mid EAS has posterior attachment to the coccyx
via the anococcygeal ligament, and the proximal EAS
becomes continuous with the puborectalis muscle. Anteriorly,
the proximal EAS forms a portion of the perineal body with
the transverse perineal muscle. There are clear differences in
the morphology of the anterior external anal sphincter that
have been demonstrated on both MRI and three-dimensional
endoanal ultrasound studies in normal male and female volunteers [17, 18]. The normal female external anal sphincter
has a variable natural defect occurring along its proximal
anterior length below the level of the puborectalis sling that
was demonstrated in 75 percent of nulliparous volunteers.
This defect correlated with ndings on anal manometry, and
the authors noted that it can make interpretation of an isolated endoanal ultrasound difcult resulting in overreporting
of obstetric sphincter defects [17]. This natural defect of the
anterior anal sphincter provides some justication as to why
anterior anal sphincterotomy is not routinely recommended
in women.
The external anal sphincter is innervated on each side by
the inferior rectal branch of the pudendal nerve (S2 and S3)
and by the perineal branch of S4. There is substantial overlap
in the pudendal innervation of the external anal sphincter
muscle on the two sides which enables reinnervation to be
partially accomplished from the contralateral side following
nerve injury [19].
Hemorrhoids
Hemorrhoids are a normal feature of human anatomy and
have been identied as present in the embryonic stage of
development [20]. While many perceive hemorrhoids as a
pathologic phenomenon, they are present in all humans and
function to improve anal continence. The pathogenesis and
treatment of hemorrhoids will be discussed elsewhere in this
book, but here we will review the features of non-pathologic
hemorrhoids.
Hemorrhoids are blood-lled cushions that line the anal
canal. Hemorrhoids are located above and below the dentate
line and have three important components: (1) the lining
(mucosa or anoderm), (2) the stroma (blood vessels surrounded by connective tissue), and (3) anchoring connective
tissue that secures the hemorrhoid to the internal sphincter
and conjoined longitudinal muscle [20]. Hemorrhoids
receive their blood supply from terminal branches of the
superior hemorrhoidal artery [21]. While it has been previously stated that the terminal branches of the superior hemorrhoidal artery end in the right anterior, right posterior, and
left lateral positions of the anal canal [20], this has been disputed [21]. At the level of the hemorrhoidal cushion, arteriovenous anastomosis (A-V shunts) exists in a complex
vascular network termed the “corpus cavernosum recti” by
Steltzner [22]. This vascular network with an arterial blood
6
J. C. Carmichael and S. Mills
supply is why pulsatile bleeding can be seen at the time of
hemorrhoidectomy.
Perineal Body
The perineal body represents the intersection of the external
anal sphincter, supercial transverse perinei, deep transverse
perinei, and bulbospongiosus (also referred to as bulbocavernosus) muscles (Fig. 1.2). Recent research, based on
advanced magnetic resonance imaging and ultrasound, has
suggested that the transverse perinei (TP) and bulbospongiosus (BS) muscles contribute signicantly to anal incontinence [23]. It has been proposed that the EAS, TP, and BS
muscles be collectively referred to as the “EAS complex
muscles.” In this theory, the EAS complex morphology is
“purse string” shaped rather than the typical “donut” shape
previously considered. When these muscles are considered
as a functional unit, it lends further support to the idea that it
is critical to attempt to repair the perineal body during overlapping sphincter reconstructions.
Pelvic Floor Muscles
In addition to the anal sphincter and perineal body, the levator ani (LA) muscles contribute to pelvic organ support. For
example, injury to the LA is seen in 55% of women with
pelvic organ prolapse but in only 16% without prolapse [24].
The LA has three subdivisions including the pubococcygeus
(aka pubovisceral), puborectalis, and iliococcygeus. Some
authors had previously suggested that the puborectalis was
part of the deep portion of the EAS [25] or that the LA did
not actually have three denable divisions [26]; however, a
signicant amount of evidence has been presented to the
contrary. In vivo MRI measurements in women have shown
distinct, visible muscle fascicle directions for each of the
three LA component muscles [27]. Embryology studies have
also demonstrated that the puborectalis muscle is a portion of
the LA muscle and shares a common primordium with the
iliococcygeus and pubococcygeus muscles [28].
Innervation of the levator ani muscles has been described
in detailed cadaveric studies [29]. The contemporary cadaveric studies suggest that the LA muscles are innervated by
the pudendal nerve branches: perineal nerve and inferior
rectal nerve as well as direct sacral nerves S3 and/or S4 (aka
levator ani nerve) [30]. The pubococcygeus muscle and
puborectalis muscle are primarily innervated by the pudendal nerve branches, while the iliococcygeus muscle is primarily innervated by the direct sacral nerves S3 and/or S4
(Fig.1.3).
Puborectalis Muscle
The puborectalis muscle (PRM) bers arise from the lower
part of the symphysis pubis and from the superior fascia of
the urogenital diaphragm and run alongside the anorectal
junction. Posterior to the rectum, the bers join forming a
sling. The “anorectal ring” is composed of the upper borders
of the internal anal sphincter and puborectalis muscle [1].
Contraction of the PRM sling causes a horizontal force [27]
that closes the pelvic diaphragm and decreases the anorectal
angle during squeeze. This is widely considered the most
important contributing factor to gross fecal continence.
Iliococcygeus Muscle
Iliococcygeus muscle (ICM) bers arise from the ischial
spines and posterior obturator fascia, pass inferior/posterior
and medially, and insert into the distal sacrum, coccyx, and
anococcygeal raphe. The ICM, along with the pubococcygeus
muscle, contributes to “lifting” of the pelvic oor [27].
Pubococcygeus Muscle
The pubococcygeus (PCM) muscle lies medial to the
PRM.PCM bers arise from the anterior half of the obturator fascia and the high posterior pubis. The PCM bers
are directed posterior/inferior and medially, where they
intersect with bers from the opposite side and form the
anococcygeal raphe (or anococcygeal ligament). PCM
muscle bers insert in the distal sacrum and tip of the coccyx. Portions of the PCM contribute to the conjoined longitudinal muscle. The PCM forms the “levator hiatus” as
it ellipses the lower rectum, urethra, and either the vagina
in women or the dorsal vein of the penis in men. The levator hiatus is connected to the intrahiatal organs by a fascial condensation called the “hiatal ligament” (Fig.1.4).
The hiatal ligament arises circumferentially around the
hiatal margin as a continuation of the fascia on the pelvic
surface of the levator muscle [31]. Enlargement of the
levator hiatus has been implicated as a cause of female
pelvic organ prolapse [32]. The PCM is the portion of the
levator ani that is typically injured during traumatic vaginal delivery [33].
Anatomy oftheRectum
The rectum is arbitrarily considered to have three distinct
parts: the upper, middle, and lower rectum. Although not anatomically distinct, the upper, mid, and lower rectal divisions
are important when considering surgical treatment of rectal
cancer. From the anal verge, the lower rectum is 0–7 cm;
middle rectum, 7–12cm; and upper rectum, 12–15cm [34].
However, the rectum is actually variable in length and may
Pubococcygeus muscle
Female Pelvic Floor
e
Pubococcygeus muscle
e
1 Anatomy andEmbryology oftheColon, Rectum, andAnus
7
Bulbospongiosus muscl
Iliococcygeus muscle
Puborectalis muscle
Gluteus maximus
Male Pelvic Floor
Perineal body
Ischial tuberosity
Superficial transverse
perinei muscle
External anal sphincter
Anococcygeal ligament
Tip of coccyx
Iliococcygeus muscle
Puborectalis muscle
Gluteus maximus
Fig. 1.2 Pelvic oor muscles
Perineal body
Ischial tuberosity
Bulbospongiosus muscl
Superficial transverse
perinei muscle
External anal sphincter
Anococcygeal ligament
Tip of coccyx
8
Female Pelvic Floor
Male Pelvic Floor
Perineal artery and vein
Perineal nerve
Internal pudendal
artery and vein
J. C. Carmichael and S. Mills
Superficial transverse
perinei muscle
Ischial tuberosity
Pudendal nerve
External anal sphincter
Anococcygeal ligament
Perineal artery and vein
Levator ani muscle
Coccyx
Perineal nerve
Internal pudendal
artery and vein
Inferior rectal artery
Inferior rectal nerve
Superficial transverse
perinei muscle
Ischial tuberosity
Pudendal nerve
Levator ani muscle
External anal sphincter
Anococcygeal ligament
Coccyx
Fig. 1.3 Pelvic oor nerves and blood supply
Inferior rectal nerve
Inferior rectal artery
Obturator inter
Anorectal junction
1 Anatomy andEmbryology oftheColon, Rectum, andAnus
Fig. 1.4 Pelvic oor
anatomy, abdominal view
9
Pubococcygeus
Hiatal ligament
Levator hiatus
nus
Piriformis
Puborectalis
Dorsal vein of penis
Urethra
Pubococcygeus
Anococcygeal
raphe
extend beyond 15cm from the anal verge. The upper rectum
can be distinguished from the sigmoid colon by the absence
of taenia coli and epiploic appendages.
The majority of the rectum lies outside of the peritoneal
cavity, although anteriorly and laterally the upper rectum is
covered by a layer of visceral peritoneum down to the peritoneal reection. The location of the anterior peritoneal reection is highly variable and can be signicantly altered by
disease such as rectal prolapse. Given the importance of the
location of the peritoneal reection with respect to transanal
excision of rectal tumors, one study sought to identify the
location of the anterior peritoneal reection in 50 patients
who were undergoing laparotomy [35]. It was found that the
anterior peritoneal reection was located on average 9cm
from the anal verge in females and 9.7 cm from the anal
verge in males– there was no statistically signicant difference based on gender.
Mesorectum
The origin of the word “mesorectum” is difcult to identify
and may be attributed to Maunsell in 1892 [36] but was certainly later popularized by Heald [37]. Unfortunately, the
term mesorectum is a misnomer that is not generally
acknowledged in classic texts of anatomy such as the Nomina
Anatomica [38]. In anatomic terms, the prex “meso” refers
to two layers of peritoneum that suspend an organ, and the
sufx applied indicates the target organ (e.g., mesocolon).
The term “meso” cannot be assigned to the rectum, as it
implies a mobile, suspended rectum, which may only be the
case in patients with rectal prolapse.
The mesorectum is a term employed by surgeons to describe
the fascial envelope of the rectum that is excised during surgical treatment of rectal cancer. Indeed, failure to completely
excise this envelope intact has been associated with an increased
10
’
Fig. 1.5 Fascial relationships
of the rectum
J. C. Carmichael and S. Mills
Rectovesical pouch
Peritoneum
Presacral fascia
Retrosacral fascia
Denonvilliers
fascia
Anterior
mesorectum
Prostate
Seminal vesicles
incidence of local recurrence of rectal cancer [39]. The mesorectum is contained within the fascia propria. The fascia propria is an upward projection of the parietal endopelvic fascia
that lines the walls and oor of the pelvis. The fascia propria
encloses the perirectal fat, lymphatics, blood vessels, and
nerves and is not considered a barrier strong enough to prevent
the spread of infection or malignancy [40].
Presacral Fascia
The presacral fascia is a thickened portion of the parietal
endopelvic fascia overlying the sacrum that covers the presacral veins and hypogastric nerves (Fig.1.5). It extends laterally to cover the piriformis and upper coccyx. As the presacral
fascia extends laterally, it becomes continuous with the fascia propria and contributes to the lateral ligaments of the rectum. Caudally, this fascia extends to the anorectal junction
covering the anococcygeal ligament. During total mesorectal
excision, the fascia propria is elevated sharply off the presacral fascia. Leaving the presacral fascia intact eliminates the
possibility of causing presacral bleeding.
Retrosacral Fascia
The retrosacral fascia originates at the third and fourth portion [41] of the sacrum and extends anteriorly to the posterior
layer of the fascia propria 3–5cm proximal to the anorectal
junction [42]. This tough fascia layer is surgically relevant as
it must be sharply incised during total mesorectal excision
[40]. The space posterior to the retrosacral fascia is referred
to as the supralevator or retrorectal space.
Waldeyer’s Fascia
There is signicant confusion about what Waldeyer’s fascia
represents as the eponym has been used to describe the presacral fascia, the retrosacral fascia, or all fascia posterior to
the rectum. In Waldeyer’s original description of pelvic fascia, there was no particular emphasis on the presacral component [40, 42]. While the debate continues regarding
“Waldeyer’s fascia,” it is important to simply understand that
the phrase can have the potential to mean presacral fascia,
retrorectal fascia, or both [43].
Denonvilliers’ Fascia
Denonvilliers’ fascia arises from the fusion of the two walls
of the embryological peritoneal cul-de-sac and extends from
the deepest point of the rectovesical pouch to the pelvic
oor [44]. Originally described by Denonvilliers in 1836 as
a “prostatoperitoneal” membranous layer between the rectum and seminal vesicles, Denonvilliers fascia is also pres-
1 Anatomy andEmbryology oftheColon, Rectum, andAnus
11
ent in females as part of the rectovaginal septum and is
sometimes referred to as rectovaginal fascia. It is found
immediately beneath the vaginal mucosa and is clearly what
most would consider as part of the vaginal wall. It merges
superiorly with the cardinal/uterosacral complex in females
or the rectovesical pouch in males. It merges laterally with
the endopelvic fascia overlying the levator muscle and distally with the perineal body. It contains collagen, some
strands of smooth muscle, and heavy elastin bers.
Rectoceles represent a defect in this layer that allows the
rectum to bulge anteriorly [45].
Microscopically, the Denonvilliers’ fascia has two layers;
however, it is not possible to discern two layers during pelvic
dissection [44]. In the anterior rectal plane, the mesorectum is
contained by the fascia propria which lies dorsal to
Denonvilliers’ fascia. The cavernous nerves run in neurovascular bundles at the anterolateral border of Denonvilliers’ fascia.
Lateral Ligaments
While frequently referred to by surgeons, there are two controversial points regarding the lateral ligaments of the rectum. First, do the lateral ligaments exist? Second, what do
they contain? Miles refers to division of the lateral ligaments
of the rectum in his seminal description of abdominoperineal
resection in 1908. Specically, he notes “In these structures
the middle haemorrhoidal arteries are found but seldom
require a ligature” [46]. It is interesting to note that at least
one modern cadaveric dissection study identied the presence of a middle rectal artery in only 22% of specimens [41]
which could be a contributing factor as to why Miles saw no
signicant bleeding in this area.
Total mesorectal excision, as popularized and described
by Heald, involves sharp dissection along the fascia propria
circumferentially to the pelvic oor. While acknowledging
that the middle rectal vessels are “divided as far from the
carcinoma as possible,” Heald does not mention “lateral ligaments” of the rectum at all [47].
In an extensive review of the anatomy of the lateral ligament, Church notes that it is a common misconception that
the lateral ligaments contain the middle rectal artery at all. It
appears that the lateral ligaments comprise “primarily nerves
and connective tissue” and their division without bleeding
attests to the absence of a “signicant accessory rectal artery
in this location in the majority of patients” [40].
In a separate cadaveric study, the lateral ligaments of
the rectum were identified as trapezoid structures originating from mesorectum and anchored to the endopelvic
fascia at the level of the midrectum. It was recommended
that, as lateral extensions of the mesorectum, the ligaments must be cut and included in the total mesorectal
excision (TME) specimen. It was further noted that the
lateral ligaments did not contain middle rectal arteries or
nerve structures of importance. The urogenital bundle
runs just above the lateral ligament at its point of insertion on the endopelvic fascia, the middle rectal artery (if
present) runs posterior to the lateral ligament, and the
nervi recti fibers (which originate from the inferior hypogastric plexus) course transversely under the lateral ligament to the rectal wall [48]. Other modern cadaveric
investigations note the rarity of middle rectal arteries and
the absence of clinically relevant neurovascular structures in the lateral ligaments [49].
Rectal Valves: TheSpiral Valves ofHouston
andKohlrausch’s Valve
The rst anatomic description of rectal valves is credited to
Giovanni Morgagni [50]; however, it was John Houston, an
Irish anatomist and surgeon, who presented the rst seminal
work on the structures [51, 52]. Houston described an average of three oblique valves with an upward orientation and
concave surface that were located successively on opposite
sides of the rectum that formed “a sort of spiral tract down its
cavity.” Houston theorized that these valves might aid in continence by supporting “the weight of fecal matter”; however,
this has not been substantiated elsewhere.
Modern anatomy texts usually also describe three rectal
valves (Fig.1.1) with the superior and inferior valves located
on the left side of the rectum and the more prominent middle
rectal valve on the right; however, this is not uniformly the
case [53]. Only 45.5% of patients will have the classic three
valve rectal anatomy; 32.5% will have only two valves; and
10.25% may have four valves.
After Houston’s denitive description of rectal valves in
1830, Otto Kohlrausch, a physician and scientist in Germany,
described a single mid-rectal valve in 1854 [54]. When there
are three valves, current anatomists identify Kohlrausch’s
valve as the middle one [51]. This valve is usually the largest,
located on the right and approximately 9–11 cm from the
anal verge, and some authors have suggested this valve could
serve as an intraluminal marker for the area of the anterior
peritoneal reection [55].
Anorectal Spaces
It is important to acknowledge and understand the anorectal
spaces created by the various myofascial relationships in the
pelvis as these spaces help us understand how anorectal sepsis can spread throughout the pelvis.
Perianal Space
The perianal space contains external hemorrhoid cushions,
the subcutaneous external anal sphincter and the distal internal anal sphincter. The perianal space is in communication
12
Obturator inter
ic space
Peritoneum
Levator ani
muscle
nus
muscle
Internal anal
sphincter muscle
Puborectalis
muscle
External anal
sphincter muscle
Fig. 1.6 Perianal and perirectal spaces, coronal view
J. C. Carmichael and S. Mills
Supralevator space
Pudendal
(Alcock’s) canal
Ischioanal space
Intersphincter
Transverse
fibrous septum of
ischiorectal fossa
Perianal space
with the intersphincteric space (Fig.1.6). The perianal space
has its cephalad boundary at the dentate line and laterally to
the subcutaneous fat of the buttocks or is contained by bers
extending from the conjoined longitudinal muscle often
referred to as corrugator cutis ani muscle bers. Otherwise,
the perianal space is contained by anoderm.
Intersphincteric Space
The intersphincteric space is the potential space that lies
between the internal and external anal sphincter and is continuous with the perianal space. It is of clinical importance as
cryptoglandular infections tend to begin in this area and
expand elsewhere to create anal stula [6].
Submucous Space
This space lies between the medial boarder of the internal
anal sphincter and the anal mucosa proximal to the dentate
line. It is continuous with the submucosa of the rectum. This
area contains internal hemorrhoid vascular cushions.
muscle and external anal sphincter. The obturator internus
muscle and obturator fascia make up the lateral boarder of
the ischioanal space. The posterior boundary is formed by
the lower border of the gluteus maximus muscle and the
sacrotuberous ligament. The space has an anterior boundary
formed by the supercial and deep transverse perineal muscles. The caudal boundary is skin of the perineum. The
ischioanal fossa contains adipose tissue, pudendal nerve
branches, and supercial branches of the internal pudendal
vessels. The right and left ischioanal space communicate
posteriorly through the deep postanal space between the
levator ani muscle and anococcygeal ligament (Fig. 1.7)
[56]. When the ischioanal and perianal spaces are regarded
as a single space, it is referred to as the ischioanal fossa [43].
Supralevator Space
The upper boundary of the supralevator space is the peritoneum, the lateral boundary is the pelvic wall, the medial
boundary is the rectum, and the inferior boarder is the levator
ani muscle (Fig.1.8).
Ischioanal/Ischiorectal Space
The ischioanal (also referred to as ischiorectal) space is the
largest anorectal space. It has been described as a pyramid
shape with its apex at the levator muscle insertion into the
obturator fascia. The medial boarder is thus the levator ani
Supercial andDeep Postanal Spaces
These spaces are located posterior to the anus and inferior to
the levator muscle. The supercial postanal space is more
caudal and is located between the anococcygeal ligament
and the skin. The supercial postanal space allows communication of perianal space sepsis.
ic space
Superficial postanal space
1 Anatomy andEmbryology oftheColon, Rectum, andAnus
13
Supralevator space
Ischioanal space
Intersphincter
Fig. 1.7 Communication of the anorectal spaces
Fig. 1.8 Perianal and
perirectal spaces, lateral view
Retrorectal space
Retrosacral fascia
Supralevator space
Levator ani muscle
Deep postanal space
Anococcygeal ligament
The deep postanal space (retrosphincteric space of
Courtney) [57] is located between the levator ani muscle and
the anococcygeal raphe. This space allows ischioanal sepsis
to track from one side to the other resulting in the so-called
“horseshoe” abscess.
Retrorectal Space
The retrorectal space is found between the presacral fascia
and fascia propria. It contains no major blood vessels or
nerves. It is limited laterally by the lateral ligaments of the